Wasted mice bear an autosomal recessive gene (wst) that causes motor neuron degeneration, radiation sensitivity in T lymphocytes and immunodeficiency. Recent work in our laboratory has demonstrated a 3-bp (3G) deletional mutation in the promoter (5' region) of the PCNA gene of wasted mice that is not found in control littermates. We wish to test the hypothesis that abnormal regulation of PCNA expression caused by this 3G deletion is responsible for the wst mutation and the wasted phenotype of these mice. The specific aims of this proposal are: (1) To confirm the 3G deletion as the molecular basis for the motor neuron disease in wasted mice through the use of vector-based and transgenic approaches. (2) To identify the protein(s) [and their gene(s)] that bind specifically to the 11G element in the PCNA promoter, to map the protein binding regions, and to determine mechanisms underlying motor neuron-specific function. (3) To investigate the reasons for motor neuron death in the wasted mouse: a) studies of tissues from wasted mice in terms of pathology, and apoptosis, b) in vitro studies of neuronal cells from wasted mice (for PCNA expression, apoptosis, and oxidative damage), c) studies examining a possible common pathway of motor neuronal cell death in the mouse, and d) differential display of wasted and FALS transgenic mouse cDNA. (4) To sequence PCNA promoters in ALS, FALS, and other motor neuron diseases to identify possible mutations associated with the diseases and to analyze these disorders for sensitivity to oxidative stress and PCNA expression. These experiments will test aspects of the following model: absence of PCNA expression in thymus and motor neurons of wasted mice causes cellular apoptosis; this absence of expression of mediated by a positive transfactor which can bind to the wild-type but not the wasted mutant PCNA promoter; the bound protein induces late expression of PCNA in motor neurons and T lymphocytes; ALS and FALS patients have abnormalities in this pathway either via a common SOD/PCNA circuit or via differing SOD and PCNA pathways that result in apoptosis/cell death.